1. Field of the Invention
The present invention relates to an electron emitter applicable to electron beam sources for use in various devices and apparatus that utilize electron beam, such as field emission displays (FEDs), backlight units, electron beam irradiation apparatus, light sources, electronic parts manufacturing apparatus, and electronic circuit components, as well as to a method of fabricating the same.
2. Description of the Related Art
As is generally known, the above-mentioned electron emitter is operated in a vacuum having a predetermined vacuum level, and configured such that a predetermined electric field is applied to an electron emitter (hereinafter called an emitter), whereby electrons are emitted from the emitter. In application to an FED, a plurality of electron emitters are two-dimensionally arrayed, and a plurality of phosphors corresponding to the electron emitters are arrayed with a predetermined spacing held therebetween. Among the two-dimensionally arrayed electron emitters, certain electron emitters are selectively driven so as to emit electrons therefrom. The emitted electrons collide with phosphors corresponding to the driven electron emitters. The phosphors hit by the electrons fluoresce, thereby displaying a desired image.
Specific examples of the electron emitter are disclosed in, for example, Japanese Patent Application Laid-Open (kokai) Nos. H01-311533, H07-147131, and 2000-285801 and Japanese Patent Publication (kokoku) Nos. S46-20944 and S44-26125. In the disclosed electron emitters, fine conductive electrodes are used as emitters. Since micromachining that involves etching, forming, or the like is required for forming such fine conductive electrodes, a fabrication process becomes complicated. Since high voltage must be applied for emitting electrons, ICs for high-voltage drive and like components must be used, resulting in increased component costs. Thus, the disclosed electron emitters involve a problem of high fabrication costs and an associated increase in fabrication costs for apparatus to which the electron emitters are applied.
In order to cope with the problem, an electron emitter in which an emitter is formed of a dielectric material is devised and disclosed in, for example, Japanese Patent Application Laid-Open (kokai) Nos. 2004-146365 and 2004-172087. General findings regarding electron emission in the case where a dielectric material is used to form an emitter are disclosed in, for example, Yasuoka and Ishii, “Pulsed Electron Source Using a Ferroelectric Cathode,” Applied Physics, Vol. 68, No. 5, p. 546-550 (1999); V. F. Puchkarev, G. A. Mesyats, “On the Mechanism of Emission from the Ferroelectric Ceramic Cathode,” J. Appl. Phys., Vol. 78, No. 9, 1 Nov., 1995, p. 5633-5637; and H. Riege, “Electron Emission Ferroelectrics—a Review,” Nucl. Instr. and Meth. A340, p. 80-89 (1994).
The electron emitters disclosed in Japanese Patent Application Laid-Open (kokai) Nos. 2004-146365 and 2004-172087 (hereinafter called merely “conventional electron emitters”) are configured such that a cathode electrode covers a portion of the upper surface of an emitter formed of a dielectric material while a grounded anode electrode is disposed on the lower surface of the emitter or on the upper surface of the emitter with a predetermined spacing maintained between the same and the cathode electrode. Specifically, the electron emitters are configured such that an exposed region of the upper surface of the emitter at which neither the cathode electrode nor the anode electrode is formed is present in the vicinity of a peripheral edge portion of the cathode electrode. At the first stage, voltage is applied between the cathode electrode and the anode electrode such that the cathode electrode is higher in electric potential. An electric field induced by the applied voltage brings the emitter (particularly the exposed portion) into a predetermined polarization. At the second stage, voltage is applied between the cathode electrode and the anode electrode such that the cathode electrode is lower in electric potential. At this time, primary electrons are emitted from the peripheral edge portion of the cathode electrode, and the polarization of the emitter is inverted. The primary electrons collide with the exposed portion of the polarization-inverted emitter, whereby secondary electrons are emitted from the emitter. An externally applied, predetermined electric field causes the secondary electrons to fly in a predetermined direction; i.e., the electron emitter emits electrons.
In the conventional electron emitters, in emission of electrons from the cathode electrode toward the emitter, emission of electrons occurs at a site on the surface of the cathode electrode where concentration of lines of electric force causes high electric field intensity at that site (an increase in electric field intensity at a portion of the surface of an electrode, or a conductor, as a result of concentration of lines of electric force at the portion is hereinafter called merely “electric field concentration,” and a site where “electric field concentration” occurs is hereinafter called merely “electric field concentration point”).
FIG. 18 schematically shows an example of a conventional electron emitter. In a conventional electron emitter 200, an upper electrode 204 is formed on the upper surface of an emitter 202, and a lower electrode 206 is formed on the lower surface of the emitter 202. The upper electrode 204 is in close contact with the emitter 202. In this case, only a peripheral edge portion of the upper electrode 204 is an electric field concentration point. The peripheral edge portion of the upper electrode 204 is a so-called triple junction, where the upper electrode 204, the emitter 202, and a vacuum contact.
However, since a peripheral edge portion of the upper electrode 204 is in close contact with the emitter 202, an electric field concentration point, which serves as an electron-emitting site, is limited to a peripheral edge portion of the upper electrode 204. Thus, the number of electron-emitting sites is limited. As a result, an increase in electron emission quantity is limited, since a drive voltage can be increased only to such a degree that dielectric breakdown of the emitter 202 does not occur.